#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    int dx[4] = { 0, 0, 1, -1 };
    int dy[4] = { 1, -1, 0, 0 };

    vector<vector<int>> updateMatrix(vector<vector<int>>& mat) {
        int m = mat.size(), n = mat[0].size();
        vector<vector<int>> dist(m, vector<int>(n, -1));
        queue<pair<int, int>> q;
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                if (mat[i][j] == 0) {
                    q.push({ i, j });
                    dist[i][j] = 0;
                }

        while (q.size()) {
            int sz = q.size();
            while (sz--) {
                auto [a, b] = q.front();
                q.pop();
                for (int k = 0; k < 4; k++) {
                    int x = a + dx[k], y = b + dy[k];
                    if (x >= 0 && x < m && y >= 0 && y < n &&
                        dist[x][y] == -1) {
                        dist[x][y] = dist[a][b] + 1;
                        q.push({ x, y });
                    }
                }
            }
        }
        return dist;
    }
};